It has been proposed heretofore to stabilize a laser, for example, a carbon dioxide laser system, at the center of the gain curve of a predetermined laser transition. This has been accomplished through the use of an adjustable mirror mounted on a piezoelectric transducer, so that the length of the cavity may be varied in accordance with signals applied to the piezoelectric transducer. The conventional manner of stabilization has been to dither the end mirror and to use the attendant output power fluctuation to generate a correction signal. However, these piezoelectric transducers are normally limited in frequency to about 1,000 cycles per second or 1 kilohertz. When attempts have been made to use this technique with lasers having intracavity electro-optic modulators, a stable condition at the center of the gain curve is not found because of the time varying heating of the electro-optic crystal due to the fluctuating power level in the dithered cavity; and as a result, the laser often locks at a frequency offset from the desired center of the gain curve.
Accordingly, a principal object of the present invention is to stabilize the transmitter laser in laser systems such as radar systems employing intracavity modulation, by electro-optic crystals or the like.